This invention relates to an improved extrusion apparatus having an internal deckle system.
An extrusion apparatus having deckles defining the web width, is well known. The deckles may be internal, external, or an external/internal combination such as an external boat deckle with an internal deckle member. U.S. Pat. No. 3,870,454 to Penrod exemplifies a deckle system including an external supply tube for a cooling fluid, and a fin that projects upwardly through the exit orifice into the land channel and beyond into the upstream passageway. The fin is in heat exchange communication with the cooling supply tube. In cast film extrusion, an external deckle member disadvantageously results in a comparatively larger gap between, and limits the relative positioning of, the exit orifice and chill rolls.
Also known as illustrated by U.S. Pat. No. 4,057,385 to Yazaki et al, is an internal deckle system having a cooling supply tube that moves in sliding contact with the manifold inner surface, and having a fin that projects downwardly. The Penrod and Yazaki et al patents teach the use of a cooling fluid to increase resin viscosity and thus reduce leakage.
U.S. Pat. No. 3,018,515 to Sneddon teaches a two component, internal deckle with external adjustment. One component is provided by a cylindrical head or manifold plug that precisely fits within the manifold, and a fin that extends downwardly from the manifold plug. A downstream closure wire serves as the second component.
U.S. Pat. No. 4,248,579 to Maejima teaches a two component, internal deckle with geared, external adjustment. A support rod movably disposed within the manifold, and a flag that extends from an end of the support rod into the preland channel, serve as one component, and a downstream deckle rod serves as the second component. Adjustment is provided by a rotatable shaft in threaded engagement with an internally threaded bore of the support rod. This system provides for reduced edge bead and for web width control.
GB Patent Application 2,092,512 to Maejima teaches a similar two component, internal deckle system. Variations include a support rod or manifold plug that closely fits within the manifold, and a pendent flag having a concave trailing edge.
FIG. 3 of Japanese Patent Application 60-28573 and U.S. Pat. No. 4,659,302 to Maejima teach a three component, internal deckle that is similar to U.S. Pat. No. 4,248,579 to Maejima. Modifications include an upper deckle portion, an independently movable, lower deckle portion supported and controlled by a separate rod, and an inclined face on the upper deckle portion. The separately movable, lower deckle portion advantageously provides for improved edge bead reduction.
A downstream deckle rod serves as the third deckle component of this type of apparatus. In the '302 apparatus, a tongue-shaped protrusion extends downwardly from the tip of the deckle rod for preventing the formation of edge bead, and a drain hole is provided for removal of resin that leaks behind the upper and lower deckle portions despite a snug fit with the flow passageway.
A drawback with the separately moveable, lower deckle portion of this type of apparatus is its sensitivity to deflection during adjustment, with bending of the support rod typically necessitating operation shut down. Additionally, bending may also result from flow pressure on the end face of the lower deckle portion or from the pressure of leaking resin on the support rod.
Also sensitive to deflection is the deckle rod. Bending of the deckle rod may break the width-controlling seal provided by the deckle rod, with resulting resin leakage through the exit orifice.
A further drawback is the tendency of stagnation and build up of resin that leaks behind the upper and lower deckle members, with residual resin build up on or near a support rod or deckle rod hindering rod movement. Deleterious degradation of resin and deposit may additionally produce aesthetically unacceptable striations on the web surface.
Leakage of resin through the end plates and around support rods for deckle members also needs to be better controlled. Also, the extrusion of a web of inconsistent width, more particularly a web having a wavy or scalloped edge, needs to be overcome.
Thus, there continues to be a need for an improved extrusion apparatus that includes an internal deckle system.